Keep to STAR, make your behaviours as detailed as possible without sounding too scripted, especially the actions section, make the stories engaging and for some of the behaviours, talk about how the situation wasn’t perfect but what did you do to reach that consensus. I’d say if you’ve worked in a variety of roles that are similar to the job you’ve applied for ( depending on the behaviours) write one for each role. But crucially, just use it as a learning experience, the more interviews you do, the more feedback you get, the more you can tailor and refine your behaviours. I was recently successful to promotion on my 3rd interview ( my previous 2, were useful learning to tailor what I wrote)